1. Field of the Invention
The present invention relates to service flow processing in a network, for example, a Hybrid Fiber Coax (HFC) network, and more particularly, to a method and apparatus of processing a multicast service flow for a headend cable modem in an HFC network using a channel bonding scheme.
This work was supported by the IT R&D program of MIC/IITA [2006-S-019-02, The Development of Digital Cable Transmission and Receive System for 1 Gbps Downstream].
2. Description of Related Art
A Hybrid Fiber Coax (HFC) network is a network including an optical fiber and a coaxial cable, and is a broadband transmission network to transmit a data signal (for the Internet, a cable television (TV), crime prevention, disaster prevention, remote inspection of a meter, and automatic control) using the optical fiber to a broadcasting station and an Optical Network Unit (ONU), and using the coaxial cable from the ONU to subscribers.
Internet Protocol (IP) multicast denotes a point-to-multipoint transmission scheme to transmit a packet to a specific service group, and includes an Any Source Multicast (ASM) scheme of classifying a session by only a receiving group address without identifying a transmitter, and a Source Specific Multicast (SSM) scheme of classifying the session by the transmitter even in the case of the same receiving group address, based on a configuration form of a multicast session.
FIG. 1 illustrates a multicast concept in Data Over Cable Service Interface Specifications (DOCSIS).
Referring to FIG. 1, all multicasts of an ASM scheme and an SSM scheme need to be supported in DOCSIS 3.0 being a standard of a cable network supporting channel bonding.
A headend Cable Modem Termination System (CMTS) 101 attaches a Downstream Service Identification (DSID) to all coming multicast service flows. The CMTS 101 transmits, to cable modems (CMs) 104 and 105, multicast service flows 102 and 103 to which the DSID is attached.
The CMTS 101 following DOCSIS 3.0 assigns the unique DSID to all multicast traffic composing the multicast session, and transmits the multicast service flow 102 to the CM 104, and the CM 104 performs filtering based on the DSID without identifying a group address with respect to the multicast session.
However, according to pre-DOCSIS 3.0, the CM 105 controls whether a multicast packet is transmitted, using a snooping operation of a protocol unit to join in a multicast group and leave from the multicast group.
In DOCSIS 3.0 using a channel bonding scheme, the CMTS 101 needs to classify a service flow so that the CM receiving a packet with respect to a single multicast session may not overlappingly receive the packet of the same multicast session.
A single multicast packet coming from a network service interface to the CMTS 101 may generate at least one multicast service flow based on a physical form (in the cable network) of a receiving group at which the multicast session intends to arrive.
Accordingly, a multicast packet processor (not shown) located in a Media Access Control (MAC) layer of the CMTS 101 needs to identify the multicast session corresponding to the multicast packet, identify the multicast service flow allocated to the identified session, compose an internal information header included in the inputted packet based on related information of the service flow, copy a plurality of multicast data packets, and transmit the plurality of multicast data packets to the CM.